THE TRANSPORTATION OF GASES 187 Brick stacks may be figured on a basis of $12 per thousand for laying with masons at $0.55 per hour.1 The cost of concrete stacks is about 5 to 10 per cent less than brick. REFEEENCES: Gustav Herrmann, "Die Graphische Theorie der Turbinen und Kreiselpumpen." Julius Hitter von Hauer, " Ventilationsmaschinen der Bergwerke" and "Die Wettermaschinen." Louis Ser, "Traite* de Physique Industriale," pp. 668-723. J. Boulvin, "Cours de Me*canique Applique* aux Machines." 3ryan Donkin, "Experiments on Centrifugal Fans," Proc. Inst. C. E., vol. cxxii, part 4,1895. Charles H. Innes, "The Fan." Simons, "Compressed Air/' McGraw-Hill. Peele, "Compressed Air Plants/' Wiley. Harris, "Compressed Air Theory and Computation," McGraw-Hill. Innes, "Air Compressors and Blowing Engines," Van Nostrand. Thorkelson, "Air Compression and Transmission," McGraw-Hill. Von Ihering, "Die Geblase," Springer, Berlin. Hirsch, "Die Luftpumpen," Janecke, Hanover. Ostertag, "Kolben und Turbo-compressoren," Springer, Berlin. Zerkowitz, "Ther-modynamik der Turbomaschinen," Oldenbourg, Berlin. COMPRESSION, STORAGE AND TRANSPORTATION OF GASES BY A. CRESSY MoRRisoN2 The problem of compressing gases is a complex one because of the great differences between them. Gases vary far more widely among themselves in their physical and chemical characteristics than do either liquids or solids. There is 50 per cent more difference between the relative specific gravities of carbon dioxide and hydrogen than there is between the weight of water and of mercury, or of lead and white pine. Nitrogen is an inert, passive, dead substance. Fluorine is one of the most energetic substances in nature. Hydrogen, nitrogen and chlorine are chemical elements. Acetylene, hydrogen chloride and methane are combinations of two or more elements. Oxygen is the supporter of both animal and vegetable life. Cyanogen is the most actively poisonous substance known. Fire or burning is a combination of fuel with oxygen. Carbon dioxide is used as a fire extinguisher. Nitrogen will not burn. Hydrogen burns with a colorless flame and acetylene possesses 240 candlepower. A gas explosion is a combination or association of oxygen with a fuel. A gunpowder or a dynamite explosion is a dissociation of nitrogen from the other elements in the explosive. Hydrogen chloride is an exceedingly strong acid. Ammonia is an almost equally strong alkali. Methane is neutral. Carbon dioxide has a negative heat value of 14,500 B.t.u. for each pound of contained carbon. Hydrogen has a positive heat value of 62,100 B.t.u. per pound, being greater than that of any other known substance. Carbon dioxide is so heavy that it can be left for a time in an open bucket, or beaker, or can be siphoned or poured like water from one vessel to another. Hydrogen is the lightest of all substances—is used for balloons—and at the same time in chemical action is just as distinctly a metal as is zinc, copper, iron or silver. Oxygen is the most abundant substance in the universe. Krypton and xenon are so rare as almost to leave doubts as to their existence. Methane is practically insoluble in water. Ammonia is absorbed to the extent of 1,000 times the volume of water. Chlorine may be liquefied and solidified with very meager pressures, and at atmospheric temperature. It is doubtful if hydrogen or methane have ever been even liquified, certainly not without the most extreme conditions of pressure and refrigeration. 1 Further cost data may be found in Gebhart's "Power Plants," Wiley, 1912. 2 Secretary of International Acelytene Assn.